Device for simultaneously producing a plurality of television information signals



K. TEER NEOU Oct. 6, 1959 DEVICE FOR SIMLTA 2,907,8l7 SLY PRODUCING A PLURALITY INFORMATION SIGNALS OF TELEVISION 2 Sheets-Sheet l Filed Oct. 25, 1954 INVENTOR KEES TEER BY@ 40 AGENT 2,9o7,s7 PLJRALITY K. TEER EOUSLY PRODUCING A Oct. 6, 1959 v DEVICE FOR SIMULTAN OF' TELEVISION INFORMATION SIGN 2 Sheets-Sheet 2 Filed Oct. 25, 1954 mam &

INVENTOR KEE EER 8% 4'- AGENT i colour television and in Stereo television.

Zfihhi? Fatenied Get. 6, 1959 DEVICE FOR SINIULTANEOUSLY PRODUCING A gllslTY OF TELEVISION INFORMATION Kees Teen Eindhoven, Netherlands, assgor, by mesne assgnments, to North American Philips Company, Ene., New York, N.Y., a corporation of Deiaware p Application October 25, 1954, Serial No. 464, 541

Clains priority, application Netherlands November 14, 1953 5 laims. s (CI. 17 8-5.4

For reproducing a scene in substantially natural colours colour' television requires, at the receiving end, the presence of information about brightness and colour of the scene concerned. Systems are known in which such information is emitted by the transmitter in time sequence and other systems in which such information is emitted simultaneously. In the latter case the signals relating to the different kinds of information required are to be produced simultaneously at the transmitting end; in the former case this may likewise take place simultaneously, each signal then being emitted only during determined periods, but it is not Strictly necessary. The information signals may in this case be produced, for example, with the use of a black-and-white television camera having alternately arranged in front of it filters which each pass only a determined colour Component of the light originating from the scene. If the requiredinformation signals are to be produced smultaneously, use may be made of a television pick-up camera comprising (in the case of three-colour television) three pick-up tubes each having a filter passing a determined prirnary colour. The signals produced by the three pick-up tubes may now be transmitted together with the required synchronisation sgnals. If desired, it is also possible to transmit linear combinations of the signals thus produced.

The object of the invention is to provide a device in which a plurality of television signals are produced by one pick-up tube for cases in which a plurality of television information signals are produced simultaneously as in s s This atfords the advantage not only that the number of pick-up tubes is smaller than that without the use of the invention, but also that a plurality of television sgnals are produced in scanning a plurality of images of an object about which the television signals must contain information with the use of one cathode-ray beam. As is well-known, in colour-television and Stereo-television receivers the superposition of the various partial images for producing the ultimate picture is a measure of the quality of this picture. In order to arrive at a satisfactory superposition, it is necessary inter alia that the scannng frames written by the various cathode-ray beams should be identical as far as possible bo-th at the receiving and the transmitting end. The smaller the number of different scanning frames, the smaller thepossibility of difierences between the scanning frames.

According to the invention, the device comprises mean by which in scanning at least one image of an object about which the television signals must contain information, which image is produced by an optical system with limited definition on the photo-sensitive screen of a pickup tube, a carrier-wave is produced in the output circuit of the pick-up tube, on which a signal relating to the image concerned is modulated, the frequency of the carrier-wave and the limitation of the definition of the image being such that a separation sufficiently free from interference between the frequency range of the modulated carrier wave or at least the frequency range of one sideband thereof and the frequency ranges occupied by modulated carrier waves produced in an analogous manner or by signals not modulated on a carrier wave is possible with the use of electric filters.

In order that the invention nay be readily carried into effect, it will now be described with reference to the accc-mpanying drawings, given by way of example, in which:

Fig. 1 shows a device according to the invention.

Fig. 2 shows a lattice such as used in the device of Fig. 1.

Fig. 3 shows the signal produced in the output circuit of the device shown in Fig. 1.

`Z'Figs. 4 and 5 also show devices according to the invention. i

Fig. 6 shows the signals produced in the output circuit of the device shown in Fig. 5, and

Fig. 7 shows a lattice as may be used in the device of Fig. 5.

Fig. l shows diagrarnmatically one embodiment of a device according to the invention intended for produciug two colour signals. 1 indicates a pick-up tube of the type known under the name picture iconoscope, 2 indicating the photo-sensitive screen thereof. An electron gun 4 produces a beam scanning in the usual manner a screen 3a under the action of deflection means (not shown), resulting in a television signal being produced in known manner across an impedance 5 connected to a signal plate 3b. It is noted that the kind of pick-up tube has been chosen quite arbitrarily and that any other pick-up tube may be imagined to be substituted in the figure. The optical system, which is shown diagrammatically only, comprises a lens 6 producing an image of the object, for example a living scene or a colour film picture, with limited definition, on a plate 7 which is again shown separately in Fig. 2. The plate 7 consists of material passing, for example, red light throughout its surface, but also passing green at determined areas only. Thus, in Fig. 2, the strips a pass both red and green light and the strips b only transmit red light and do not transmit green light `,or to a very small extent only. This implies that plate 7, on the one hand, does hot constitute an obstacle for the incident red light and, on the other hand, fulfils the function of a lattice for the incident green light. The plate 7 is now sharply projected on the photo-sensitive screen 2 with the use of a lens 8, resulting in a charge image being produced on screen a due to photo-emission of screen 2. It is to be noted that the strips a and b are at angles %0 with lines corresponding to the scanning lines written on the screen 3a by the cathode-ray beam.

In scanning the screen ?a by means of the cathode-ray beam several signals occur across the impedance 5. The image on screen 2, produced by the red light, provides a signal S across the impedance S which in regard to frequency extends from O to a frequeney n (The directcurrent Component must, as usual, be added to the signal in a ditterent manner known per se). The fact that the signal S does not extend throughout the frequency range of the pick-up tube is due to the object being reproduced on the plate 7 with limited defintion only. This limitation of frequency is not objectionable, since television information signals are in most cases limited in frequency, inter alia in connection with the available bandwidth of the transmission path.

The image on screen 2 produced by the green light results in a charge image on the screen 301 and this provides in scarning a signal across the impedarce 5, which signal, as known per se, comprises, on the one hand, a signal proportional to a signal aswould be produced in scanning an image which has not passed a lattice and, on the other hand, a carrier-wave on which this signal is modulated, since the lattice for the green light may be written in Fourer development:

c -l-c cos 27%-1-0 cos 2.2vr l-j- -wherein l is the period of ,the lattice and x the distance between a :point on the lattice and the zero point in a .direction parallel to the scanning direction r (see Fig. 2). An analogous expression is found for an image of the said lattice on the photo-sensitive ,screen 2. When the image of the object on the lattice may be represented on the line r by f(x), the total light distribution along the considered line, as far as the green light is concerned, may thus be written as:

f(x)[c +c cos 27%-1-0 cos 2.27&

.and the light distribution along the corresponding line on the photo-sensitive screen 2 as:

Af(px)[c +c cos ?mg-Faces 2.21r%+ wherein p represents the ratio between a determined distance on screen 2 and the corresponding distance on the lattice. If, now, the charge image of such a -line is scanned at a speed v, the signal across the impedance 5 may be written as:

signal proportional to the signal which would be produced in scanning an image which has not passed a latvtice, and Bc f(vt) cos 27rn CS cos 27rn t represents a carrier-waveof frequency n on which the said signal is modulated( i As 'will -appear hereinafter, the higher harmonics of this carrier wave which also occur are negligible. At a givenscanning speed v, it is necessary for l and f(x) to be so chosen that the frequency spectrum of .S and of CS cos 21rn t do not overlap or at least overlaptoso small an extent that the further use of the information signals obtaned in a manner which will be described herenafter is not interfered thereby. l is determined by the lattice and f(x) by the definiton of the image produced ,on the lattice.

Fig. 3 shows the frequencyrspectrum of the sgnals thus produced. As a matter of fact, the maximumfrequency occurring in the signal S is, in the chosen example, equal to the maximumfrequency occurring in the signal.S since the corresponding images are reproduced on the lattice7 with equaldefinition. i The signals S and 8, may beindividually obtaned from the signal occurring across impedance 5 in, the following manner. The output signal across impedance .5 is supplied, on the one hand, to .a band-pass filterP havingcut-off frequencies ,n -n andn +n and, onthe other hand, to a low-,pass i filter F having acut-off frequency n nal of F is .supplied to a detector D the signal S occurring across output terminal P, which signal is supplied, if desired after amplication, to an The output sig- This results in adding device A which has :also supplied to it the output signal S -j-s of .the filter 1 Sri-& and S are subtracted from one another in A resulting in'the signal 8,. occurring across the output Q. p

It will be evident that in `connectior with the filters F and F the higher harmonics of the' carrier wave of frequency n are immaterial.

It is noted that, instead of produeing a sharp image of plate 7 on the screen 2, it is naturally also possible for plate 7 to be arranged itself on the screen 2; in the formulas this implies that p is chosen to be equal to l. 'Lens 8 is not required in this case.

Furthermore, it is possible to make the photo-sensitive screen 2 fulfil itself the function of plate 7, viz. by' composing the photo-sensitive layer of strips' similar'td the stripsof plate 7, determined strips being sensitivetojffor example, red and green and others being sensitive to green only and not sensitive -to red or at least to a small extent.

It is possible both in the case of the colour filter shown in Fig. 2 'and in the case of the photo-sensitive screen which itself fulfils the function of plate 7 that the kind of light which has to be transmitted by allstrps or which has to lead to emission `on allstrips leads for the strips having to transmit one colour onlyor'for the strips sensitive to one colour only to results which are different from .those for the strips having to transmit both colours or having to be sensitive to both colours. Thus, for example, the plate 7 may attenuate the red lighton the strips af to a greater extent than on the strips b. An even illumination ofthe plate 7 by red light then does not result in an even charge image on screen 3a. This implies ,that 'not only S but also a fraction of S, is modulated on the carrier wave. Demodulation of the carrier wave then provides, instead of S alone, also a firaction of S viz. aS wherein a represents aconstant. The output signal of filter F was S -I-S It will be evident 'that the signals S and S may be found from the signals S +aS and S +S, with the aid of of linear combinations similar to those described with reference to Fig. 1. However, it is possible to correct already before the demodulation .of the carrier wave, for example by giving a higher int'ensity to the scanning cathode-ray beam onthe strips .of the charge image on which 'the charge is smaller than with an even charge image as would be due' to occur by the action of an even illumination.

Fig. 4 shows an embodiment according to the invention adapted for Stereo-television. Identical parts of Figs. r 1 and 4 are indicated by the same reference numerals. The object is projected with limited definition, on the one hand, on the screen 2 with the use of' lenses 9:1 and 9b and, on the other hand, projected with limited definition on a lattiee 11 with the use of a lens' 10. In' this case the lattice is built up from material of which, for example, the strips a (see Fig. 2) pass the whole visible spectrum and the strips b are opaque for this whole spectrum. The image of the said lattice is also projected with the use of a lens 12 and through a system of semitransparent mirrors H on the screen 2 of the pick-up tube. The signal produced across the impedance 5 is similar to that described with reference to Fig. l and the two signals, which contain different information about the object, may be obtaned in a similar manner as indicated hereinbefore. j

As a 'matter of fact, a device intended for producng two colour signals may likewise comprise two jspatially separate light-paths as in the device shown in 'Fig. 4. However, it is then necessary to provide colour filters in the two light paths.

i For simultaneously producing three information signals about the same object intended for three colour television, it is possible to produce two signals in the abovedescribed manner with the use of a pick-up tube and the third signal with the use of a separate pick-up tube.- If

necessary, linear combinations may be formed from the signals .thus obtaned. The brightness 'signal will advantageously be 'chosen for the third signal'. It is thus avoided that in composing the brghtnesssgnal of three signals, each relating to a primary colour of the object, misregistration of the bn'ghtness may-occur in the image "ultimately reproduced, which is very' *troublesome In "this connection it is to be considered that misre'gistration u u ?of brightness is considerably more interfering than misregistration of colour. However, it is alternatively possible to produce the three signals with the use of one pick-up tube. Fig. 5 shows an embodiment of the invention in which three information signals are produced with the use of one 'pick-up tube. 1 indicates, as before, the pick-up tube comprising the photosensitive screen 2, screen 3a and 'the signal plate 3b, 4 indicates the electron gun and 5 :indicates the impedance from which the output signal of the pick-up tube is derived. Lens 13 produces of the object with the use of the semi-transparent mirror systems l-I and H on the one hand, an image of limited definition via light path L and a lens 18 on the screen 2 and, :on the other hand, images of limited definition via light paths L and L including colour filters 14 *and 15, on lattices 16 and 17. The lens 18, in` turn, produces sharp images of the lattices on the screen 2. The fineness of ?the lattices is chosen dillerently, that is to say such that in scanning the screen Sa, the signal across impedance 5 exhibits, for example, a frequency spectrum as shown in Fig. 6. The image produced via light path L yields ?the signal portion S for example of large bandwidth, and provides, for example, the normal black-and-white information about the object. It is alternatively possible to provide a colour filter, for example a green filter, in the light path L the image then naturally providing 'information about the green light emitted by the object.

If filter 14 passes red light only, the image produced by the light path L provides a signal S for example of small bandwidth, according to the definition of the image produced on the lattice 16, and a signal S, cos 21-n t with information about the red light emitted by the object. If filter 15 passes blue light only, the image produced via light path L yields signals S if desired likewise of small bandwidth, and signals S cos zv-n t with information about the blue light emitted by the object. The frequency ranges of S cos 27rn t and S cos 21rn t may overlap between the frequencies n and 2, as shown in the figure.

The output signal of the pick-up tube across the impedance 5 is supplied to three filters F F and F F :is a low-pass filter having a cut-oli frequency n F is a 'bandpass filter having cut-oil frequencies 715 and a frequency slightly higher than n and F is a bandpass filterhaving cut-oli frequencies 11 and a frequency :slightly lower than 712. The output signals of F and F :are supplied to demodulators D and D 'across output terminals R and T of which the signals S and S occur. The signals S and S if desired after amplification, are combined in proper size and phase with the output signal of F in an adding device Az, :for example in such manner that the signals S and S initially present ther-ein are just absent, or in such manner that a desired combination of S S and S occurs at the output terminal V.

It will be evident that the function of colour filter 14 and lattice 16 may be fulfilled by a plate positioned at the area of lattice 16, of which determined strips only transmit red light and the other strips are fully opaque. The same remark naturally applies to colour filter 15 and lattice 17. If desired, the semi-transparent mirror systems may have a colour-Sorting action.

It is also possible to ccmbine the light paths L and L by causing the functions of colour filters 14, 15 and lattices 16, 17 to be fulfilled by a plate as shown in Fig. 7a, which is arranged at the area of one of the initial lattices 16 and 17. In Fig. 7a, the strips a with left-hand cross hatching transmit red light only, the strips c With righthand cross-hatching transmit blue light only, the strips b with double cross-hatching transmit red and blue light and the strips d without cross-hatching are opaque. Fig. 7b shows in what manner the plate of Fig. 7a behaves for red light and Fig. 7c shows in what manner the said However, it is in this' ,case necessary to utilise single sideband detection.

plate behaves for blue ligh. When using a plate as shown in Fig. 7a, the semitransparent mirror systems may be of simpler design, since in this case one of the light paths Lz and L is not required.

If the light path L initially also contains a colour filter, for example a green filter, the number of light paths may be reduced to one by providing for all strips a, b, c, d of the plate shown in Fig. 7a to be transparent for green light. In this case the semi-transparent mirror systems may be completely dispensed with. If desired, it is possible, as before, to arrange the plate on the screen 2 and in this case also the screen 2 may fulfill the function of the plate.

It is naturally possible to produce images of an object only via two or more lattices, that is to say no image without the intermediary of a lattice -as in the device shown in Fig. 5. In such a case it is su'icient to detect the various modulated carrier waves. It is thus not necessary to form linear combinations with unmodulated signals occurring across the impedance 5 and, furthermore, the direct-current components are present in the demodulated signals and thus need not be introduced. If desired, it is naturally possible to form linear combinations from the signals found by d emodulation of the various carrier waves.

What is claimed is:

l. Apparatus for converting a plurality of different visual aspects of television information into correspouding electrcal'signals, comprising a photoelectric pick-up tube having a scanned photo-sensitive screen and a signal output electrode, a lens system having limited definition, means for projecting a first one of said visual aspects through said lens system and onto the entire surface of said screen, means for projecting another of said visual aspects onto said screen in a periodical. lattice pattern which periodically crosses the scanning pattern of said screen, and means for scanning said screen thereby to produce at said output electrode a first signal corresponding to said first visual aspect and having a relatively low frequency range as determined by said limited definition, and a second signal having an unmodulated Component lying at least in part in said relatively low frequency range and a Component which is modulated on a carrier wave; said carrier wave being produced by the scanning of said lattice pattern and the frequency of said carrier wave being dependent upon the periodicity of said lattice pattern, said lattice pattern having a periodicity sufficiently great with respect to the value of said limited definition so that said modulated carrier wave occupies a frequency range which lies partly within and partly outside of said relatively low frequency range.

2. Apparatus as claimed in claim l, in which said means for projecting said visual aspects onto said screen conprises a color filter positioned in the optical path of said pick-up tube and adapted to pass over its entire surface said one visual aspect and to pass over periodically arranged portions of its surface said other visual aspect,

3. Apparatus as claimed in claim 2, in which said color filter is arranged on said photo-sensitive screen.

4. Apparatus as claimed is claim 1, including a first electrcal filter which passes only frequencies in the frequency range of said modulated carrier wave, a second electrcal filter which passes only frequencies in said relatively low frequency range, a detector, and a subtracting stage, said first electrcal filter being connected between said output electrode and said detector, said second electrical filter being connected between said output electrode and an input of said subtracting stage, and means connected to feed the detected output signal from said detector to an input of said subtracting stage.

5. Apparatus as claimed in claim 4, including means for projecting a third visual aspect onto said screen in a periodical lattice pattern which periodically crosses the scanning pattern of said screen with a different periodicity from that of said first-named lattice pattern thereby caus- 

